Nucleotide sequencing of genes coding for E. coli, S. typhimurian and M. luteus DNA topoisomerase I is to be carried out. The biological roles and the regulation of E. coli DNA topoisomerase I will be studied by the methods of molecular genetics. DNA topoisomerases from yeast and Drosophila are to be purified and the genes coding for these enzymes are to be identified by a combination of immunological and recominant DNA methodology. Mechanistic studies on DNA gyrases and E. coli DNA topoisomerase I will be continued at the level of protein-DNA interactions. The structure of The origin of replication of the single-stranded fd DNA is to be investigated by physiochemical and genetic analyses. Studies on interactions between this origin and E. coli RNA polymerase and the single-stranded DNA binding protein are to be continued.